I put cm7 on my wife's vibrant several weeks back. I myself, have been using cm7 on all my phones since the beginning. Even on the stock tmo rom, I had to modify her supl information to fix the gps locking problem. Well, that portion has been fixed in cm7, but she now had a different problem. I found a solution from another forum that worked. she locked on 7/8 sats in <1 min. tested after 2 more reboots and she was still able to lock. note the top of this post that you will see an error, but it still works.
If this worked it was only by Placebo effect, the error you're seeing is that the partitions that you're clearing there ( /dev/block/mmcblk0p13, /dev/block/mmcblk0p14 ) don't exist on vibrant cyanogen mod. If they don't exist...clearing them won't do anything. In fact, what you're doing when they don't exist is filling up all free space on that partition with 0's. This will *not* fix a GPS on the vibrant.